Nitromethane decomposition over Cu-ZSM-5 and Co-ZSM-5

To better understand the nitromethane decomposition mechanism over Cu-ZSM-5 and Co-ZSM-5, CH3NO2 and CO adsorption on Cu-ZSM-5 and Co-ZSM-5 was studied by IR and EPR spectroscopies. After adsorption of nitromethane on H-ZSM-5, Al(iii)-NCO forms at 200 degreesC. Nitromethane adsorption on Cu-ZSM-5 forms Si-NCO and Cu(i)-NCO which are observed from room temperature to 300 degreesC. Nitromethane adsorption on Co-ZSM-5 forms Si-NCO from room temperature to 200 degreesC, and Co(ii)-NCO above 200 degreesC. We suggest that Co(ii)-NCO forms by the substitution of NCO for water in dehydrated Co-ZSM-5 from 200 to 450 degreesC. CO is adsorbed on Cu-ZSM-5 to form Cu(i)-CO (2157 cm(-1)) at room temperature. It is newly found that CO binds to Cu(ii)-O- sites in dehydrated Cu-ZSM-5 at room temperature to form Cu(ii)-O-(H2O)(CO) (2138 cm(-1)). But only Cu(i)-CO (2157 cm(-1)) remains at 200 degreesC and above. CO adsorption on Co-ZSM-5 does not bind to Co(ii) and only shows a gas phase CO IR spectrum. CO adsorbed on dehydrated Co-ZSM-5 at -196 degreesC forms weakly bound Co(ii)-CO by EPR, in which the unpaired electron is mainly located on Co(ii). Desorption of CO from Co(ii)-CO occurs by about -73 degreesC so Co(ii)-CO is not observed at room temperature.